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Alcohols

Learn about the basics of alcohols, including their naming, classification, and properties. Explore their chemical reactions, such as oxidation and esterification. This topic covers methanol, ethanol, propanol, and phenol.

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Alcohols

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  1. Alcohols Foundation in Science Mahsa University College Chem 2 Topic: Alcohol Prepared by Mr. Daniel Philip 1

  2. Alcohols An alcohol consists of a carbon chain with a hydroxy group (-OH) attached Methanol Ethanol Propanol Phenol 2

  3. 1. Naming and Drawing molecules Nomenclature of Alcohols • Alcohols are named by dropping the e ending of the parent alkane and replacing with ol. The –OH group can also be named as a substituent using the group name, hydroxy. • Still another nomenclature involves naming the alkyl group followed by a space and the word alcohol

  4. General formula of alcohols CnH2n+2O First member is Methanol a) Displayed formula is H   |  H-C-O-H |   H  b) Systematic name: methanol (from : methan + ol) c) Structural formula - CH3OH d) Molecular formula CH4O

  5. Names and Structural formula of common alcohols Examples: CH3OH Methanol CH3CH2OH Ethanol CH3CH2CH2OH is called propan-1-ol or 1-propanol CH3CH(OH)CH3 is called propan-2-ol or 2-propanol

  6. if more than one hydroxyl is present, the prefixes di-, tri-, tetra-... are used the terminal "e" is retained on the parent alkane name. CH2OHCH(OH)CH2OH Common name is Glycerol and systematic name is 1,2,3-propanetriol.

  7. Exercise 1 Give the displayed formula, structural formula, molecular formula and empirical formula of the following alcohols • 1-butanol • 2-butanol • 2-methyl-1-propanol • 2-methyl-2-propanol

  8. Name the following molecules:

  9. Alcohol Classification Alcohols may be classified as - Primary - Secondary - Tertiary Depending on whether the carbon atom that is attached to the –OH group is surrounded by one, two or three other carbon atoms 9

  10. Primary Alcohols A primary alcohol is bonded to carbon atom that is bonded also to one or no carbon atom carbon atom. 10

  11. Secondary Alcohols A secondary alcohol is attached to a carbon atom that is bonded also to 2 carbon atoms. 11

  12. Tertiary Alcohols 12

  13. Polyhydroxy alcohols Alcohols that have more than one OH group are known as polyhydroxyl alcohols. Two examples are shown below 13

  14. Name and classify the following alcohols. • 2-butanol (Secondary) • 2-propene-1-ol (Primary) • 2-methyl-1-butanol (Primary) • 2-methyl-2-butanol (Tertiary) 14

  15. Properties of Alcohols The physical properties of alcohols are similar to those of both water and hydrocarbons • The shorter chain alcohols such as methanol and ethanol are similar to water, in general they -- have higher boiling points than hydrocarbons but lower than water -- dissolve in water to some degree -- are more polar than hydrocarbons but less polar than water 15

  16. Alcohols are polar molecules Reactivity: • The image shows the electrostatic potential for methanol.  The more red an area is, the higher the electron density and the more blue an area is, the lower the electron density.  • The alcohol O atom are a region of high electron density (red) due to the lone pairs.

  17. 3. Physical properties • 1.Boiling point is higher than hydrocarbon. (Due to intermolecular H-bond) • 2. Spirituous odour with burning taste. • 3. Short chain alcohols, up till 4 carbon atoms are soluble in water. Extra info: Phenol (at room temperature) is colourless liquid but tinged with pink oxidation product. It is moderately soluble in water. It is corrosive.

  18. Exercise • Explain why ethanol liquid is soluble in water but ethane gas isn’t soluble in water. 4marks • Explain why the boiling point of ethanol is greater than the boiling point of ethane. 4marks

  19. Reactions of Alcohols • Alcohols undergo several types of reactions including: • Oxidation • Dehydration • Reactions with active metals • Esterification • Substitution 19

  20. 4. Chemical reactions of Alcohols 4.1 Alcohol with alkali metals→ alkoxide (strong base!)2 Na + 2 CH3OH → H2(g) + 2 CH3O- + 2 Na+(sodium methoxide) 4.2. Alcohol substitutionCH3CH2CH2OH + HCl → CH3CH2CH2Cl + H2O CH3CH2OH + PCl5  CH3CH2Cl + HCl + POCl3 4.3. Alcohol dehydration CH3-CH2-OH→ CH2=CH2 + H2O

  21. Chemical reactions of Alcohols 4.4 Alcohol oxidation (burning) * primary alcohols → aldehydes * secondary alcohols → ketones * tertiary alcohols → no reaction 4.5 Alcohol with caboxylic acid for Esterification reaction alcohol + acid → ester + H20

  22. 4.4 Oxidation Alcohols are oxidized to alkanals (aldehydes) or alkanones (ketones) and even carboxylic acids. 22

  23. Primary Alcohols are Oxidized to Alkanals/Aldehyde The most common oxidizing agents are acidic KMnO4 soultion or , acidic K2Cr2O7 or even oxygen from the air(very very slow). The mechanisms of such reactions are usually complex 23

  24. Secondary Alcohols are oxidized to Alkanones/Ketones Example 24

  25. Tertiary Alcohols are not easily oxidized There is no hydrogen attached to the tertiary carbon. It is not possible for a carbonyl group on the tertiary carbon to be oxidixed. 25

  26. Tertiary Alcohols are not easily oxidized Furthermore the large R groups on the tertiary carbon, prevent reacting groups. Hence tertiary alcohols are rather unreactive. 26

  27. 4.4. Oxidation Aldehyde / Alkanal Carboxylic acid Primary alcohol Common O.A. : K2Cr2O7/ H+, KMnO4/ H+ Ketone Secondary alcohol

  28. Oxidizing agents are acidified KMnO4 or acidified K2Cr2O7 Primary alcohol with acidic oxidizing agent solution, distilled, gives aldehyde Primary alcohol with acidic oxidizing agent solution, reflux boiling, gives carboxylic acid Secondary alcohol with acidic oxidizing agent solution, reflux boiling, gives ketone

  29. Observation: • acidified KMnO4 solution/acidified manganate(VII) solution : Purple to Colourless or purple is decolourised Or b) acidified K2CrO7 solution/acidified dichromate(VI) solution : Orange to Green

  30. Exercise Draw the displayed structure of the organic product formed, if any when the following alcohol was heated with acidified KMnO4 solution, reflux (boiling) • Methanol • Ethanol • 1-propanol • 2-propanol • 1-butanol • 2-butanol • 2-methyl-1-propanol • 2-methyl-2-propanol

  31. Draw the displayed structure of the organic product formed, if any when the following alcohol was mixed with acidified KMnO4 solution and the product is distilled off • Methanol • Ethanol • 1-propanol • 1-butanol • 2-methyl-1-propanol

  32. 4.3 Dehydration Many alcohols undergo intramolecular dehydration, removing water to form alkenes. 32

  33. 4.3 Dehydration Definition: removal of water from a molecule. Extra info: H and OH are removed from two adjacent carbons. Reagent and conditions:Dehydrating agents Con H2SO4, heat Con H3PO4, heat Solid SiO2, heat Solid Al2O3, heat Solid ceramic or solid pumice, heat

  34. Exercise Write an equation and then give the displayed structure of the organic product formed, if any when the following alcohol was heated with con.H2SO4 and heated(warm/boil or reflux boiling) • Ethanol • 1-propanol • 2-propanol • 1-butanol • 2-butanol • 2-methyl-1-propanol • 2-methyl-2-propanol

  35. 4.1 Reactions with Metals • Alcohols are far less acidic than water but they react with highly reactive metals such as potassium and sodium. • The metal replaces the hydrogen atom in the alcohol group forming a salt and hydrogen gas 35

  36. Note that the reaction between Na, sodium solid and alcohol at room temperature releases colourless gas of H2. This indicates the presence of OH hydroxy group in alcohols.

  37. Quick exercise Write an equation for reaction between Sodium metal at r.t. with • Methanol • Ethanol • 1-propanol • 2-propanol

  38. Esterification An alcohol reacts with an alkanoic acid to form an ester and water. 38

  39. Write an equation and then give the displayed structure of the organic product formed, if any when the following alcohol was heated with ethanoic acid with drops of con.H2SO4 and heated(warm/boil or reflux boiling) • Methanol • Ethanol • 1-propanol • 2-propanol • 1-butanol • 2-butanol • 2-methyl-1-propanol • 2-methyl-2-propanol

  40. Exercise Ethanol undergoes the following reactions: Reaction 1: Ethanol Ethene Reaction 2: Ethanol  Ethanal Reaction 3: Ethanol  Ethanoic acid Reaction 4: Ethanol  CH3CH2ONa Reaction 5: Ethanol  CH3CH2CO2CH2CH3 Reaction 6 : Ethanol to CH3CH2Cl • Name the type of organic reaction in reaction labelled as: 1:………………………………… 2 :………………………………… 3 :………………………………… 4 :………………………………… 5 :………………………………… 6:…………………………………

  41. Ethanol undergoes the following reactions: Reaction 1: Ethanol Ethene Reaction 2: Ethanol  Ethanal Reaction 3: Ethanol  Ethanoic acid Reaction 4: Ethanol  CH3CH2ONa Reaction 5: Ethanol  CH3CH2CO2CH2CH3 Reaction 6 : Ethanol to CH3CH2Cl b) Give the reagents and conditions for reaction labelled as 1:………………………………… 2 :………………………………… 3 :………………………………… 4 :………………………………… 5 :………………………………… 6:………………………………….

  42. Ethanol undergoes the following reactions: Reaction 1: Ethanol Ethene Reaction 2: Ethanol  Ethanal Reaction 3: Ethanol  Ethanoic acid Reaction 4: Ethanol  CH3CH2ONa Reaction 5: Ethanol  CH3CH2CO2CH2CH3 Reaction 6 : Ethanol to CH3CH2Cl C) Give the observation for reaction labelled as 1:………………………………… 2 :………………………………… 3 :………………………………… 4 :………………………………… 5 :………………………………… 6: ……………………………………..

  43. Ethanol undergoes the following reactions: Reaction 1: Ethanol Ethene Reaction 2: Ethanol  Ethanal Reaction 3: Ethanol  Ethanoic acid Reaction 4: Ethanol  CH3CH2ONa Reaction 5: Ethanol  CH3CH2CO2CH2CH3 Reaction 6 : Ethanol to CH3CH2Cl d) Name the organic products of reaction labelled as 4:……………………….. 5:……………………….. 6:………………………..

  44. Ethanol undergoes the following reactions: Reaction 1: Ethanol Ethene Reaction 2: Ethanol  Ethanal Reaction 3: Ethanol  Ethanoic acid Reaction 4: Ethanol  CH3CH2ONa Reaction 5: Ethanol  CH3CH2CO2CH2CH3 Reaction 6 : Ethanol to CH3CH2Cl e) Give the displayed formula of organic prodct formed from reaction labelled as 1: 2: 3:

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